The lifestory of Atlantic salmon is kept as a permanent record in their scales and could help efforts to protect future fish stocks, Defra-funded research has found.

The research published today in the journal Scientific Reports helps solve the long-standing mystery of where in the ocean Atlantic salmon go to feed when they leave British waters, and could shed light on why numbers have declined since the 1970s.

As with trees, the growth of salmon scales can be seen as a series of rings, with the most growth occurring when they are feeding out at sea. Scientists took a portion of the scale from when the fish was at sea, and measured the carbon isotopes which are stored in the scale as collagen. By matching the carbon levels with satellite records of ocean surface temperature, the scientists were able to predict where in the Atlantic the fish were living and feeding.

Richard Benyon, Fisheries Minister, said:

“There is so much about the habits of fish when they leave our rivers that remains a mystery. This ground-breaking research will be vital in helping us to learn about their feeding behaviour out at sea, and how best to protect their numbers for future generations.”

More than 500 scales were analysed from archived samples at the Centre for Environment, Fisheries and Aquaculture Science (Cefas) and the Centre for Ecology and Hydrology (CEH). The research found that fish from different rivers were swimming to completely different areas in the ocean when they left the British shores. For example, salmon from rivers including the River Tyne in the North East were swimming towards the Norwegian Sea, whereas fish from the River Frome in Dorset were feeding close to Iceland.

Dr Kirsteen MacKenzie, lead author of the research from the University of Sounthampton, said:

“As every single salmon contains a natural chemical tag, we can now see where fish from individual rivers go to feed in the Atlantic. We found that salmon born in two areas of the British Isles swim to feeding grounds that are far apart, and experience very different conditions while at sea.”

Co-author Dr Clive Trueman, also from the University of Southampton, continued:

“Our technique can also be used to aid conservation of animals such as turtles, seabirds and tuna, and identify the best areas for marine protection measures.”

The research was funded through a £66,000 grant from Defra. Further research is now ongoing to chart the habits of many more Atlantic salmon populations when they leave British rivers.